Performance improvements for MIOpenConvBwdWrW_GxL_1x1.cl
Performance improvements for MIOpenConvBwdWrW_GxL_1x1.cl

Also contains perf w/a to pre-calculate g_data pointer with
offset to help vectorization.

ROCmSoftwarePlatform/MIOpen,ROCmSoftwarePlatform/MIOpen,ROCmSoftwarePlatform/MIOpen,ROCmSoftwarePlatform/MIOpen,ROCmSoftwarePlatform/MIOpen